1. Field of Invention
The present invention relates to a pixel structure. In particularly, the present invention relates to a method for repairing the pixel structure and a thin film transistor structure in the pixel structure.
2. Description of Related Art
The media technology in modern societies is rather prosperous, mostly benefiting from rapidly advancing of the semiconductor devices and display apparatuses. Owning extraordinary features such as high resolution, splendid space utility, low power consumption, free of radiation and so forth, the thin film transistor liquid crystal display (TFT-LCD) has gradually become dominant as the mainstream in the display marketplace nowadays.
In general, the TFT-LCD is mainly composed of a thin film transistor (TFT) array substrate, a pair of facing substrates, and a liquid crystal (LC) layer disposed between these two substrates. Here, the TFT array substrate mainly comprises a substrate, a plurality of TFTs arranged in matrix on the substrate, pixel electrodes, scan lines and data lines. Generally speaking, the scan lines and data lines are used to transfer the signals to the corresponding pixel structure for displaying images.
FIG. 1 schematically shows a local view of a traditional pixel structure in the prior art, and FIG. 2 schematically shows a cross-section view with reference to the section line A-A′ in FIG. 1. Please refer to FIGS. 1 and 2 simultaneously. The traditional pixel structure 120 mainly comprises a TFT 122, a pixel electrode 124, a scan line 126 and a data line 128. The TFT 122 is electrically connected to the pixel electrode 124. Specifically, the TFT 122 on the substrate 110 mainly comprises a gate 122a, a channel layer 122b, a source 122c and a drain 122d, as shown in FIG. 2. The structure of this TFT 122 is belonged to the bottom gate type, and the drain 122d of the TFT 122 is electrically connected to the pixel electrode 124. As can be seen in FIG. 1, the scan line 126 and data line 128 can be used for transferring a proper voltage via the TFT 122 to the pixel electrode 124 such that the displaying of images is achieved.
It's worthy to note that the effect of gate-to-drain parasitic capacitor (Cgd) is usually induced on the overlapping area 10 of the gate 122a and drain 122d. This value of gate-to-drain parasitic capacitor Cgd is directly proportional to the area of the overlapping area 10. In manufacturing TFTs, due to alignment-error of photo-masks, vibration of the machinery or other factors, the changing of the overlapping area 10 of the gate 122a and drain 122d would occur, and it causes the variation of the value of gate-to-drain parasitic capacitor. Nevertheless, the pixel feed through voltage tends to vary responding to this variance of the value Cgd, and the displaying quality of the TFT-LCD suffers from the variance of the pixel feed through voltage.
Furthermore, due to the errors during the fabricating process that would sometimes cause defects in part of the pixel structure, an act of repairing the pixel structure with defects is performed. Take one for example. Mostly, when TFT-LCD is under the normally white mode, the method of repairing the pixel structure 120 is to electrically connect the drain 122dand the scan line 126 so that the scan line 126 can be electrically connected to the pixel electrode 124 via the drain 122d. By doing so, dot defects of the pixel structure 120 can be repaired as dark points. For the real cases, however, as result of the over-twisting of liquid crystal polymers inside TFT panel, caused by the over large voltage difference across the scan line 124(the pixel electrode 124) and the electrode on the facing substrate, the pixels with defects appear grey points and they are unable to be repaired as dark points.